Method for transcoding audio signals, transcoder, network element, wireless communications network and communications system

ABSTRACT

The invention relates to a method for transcoding audio signals in a communications system. In order to improve the inter-operability between units ( 2,40 ) capable of handling wideband audio signals and units ( 3,46 ) or network components ( 50 ) capable of handling narrowband audio signals, it is proposed that first, an audio signal is received in a network element ( 42 ) of a communications network via which said audio signal is transmitted. Next, it is determined in said network element ( 42 ) whether a transcoding of the received audio signal is required. In case a narrowband-to-wideband transcoding of the received signal is required, the received narrowband audio signal is transcoded into a wideband audio signal in the network element ( 1,42 ). The generated wideband audio signal is then forwarded to the receiving terminal ( 2,40 ). The invention equally relates to a corresponding communications system and its components.

FIELD OF THE INVENTION

[0001] The invention relates to a method for transcoding an audio signalin a communications system, which audio signal is to be transmitted to areceiving unit via a communications network. The invention equallyrelates to a transcoder, to a network element comprising a transcoderand to a wireless communications network and a communications systemcomprising a network element with a transcoder.

BACKGROUND OF THE INVENTION

[0002] In conventional telecommunications systems, the bandwidthemployed for transmitting speech signals has typically been limited to afrequency range of about 300 to 3400 Hz with a sampling rate of 8 kHz.This limitation applies to normal PCM (pulse code modulation) speech,which employs a 64 kbit/s coding defined in specification ITU-T G. 711,as well as to most of the low-bit rate speech coding methods used intelecommunications systems.

[0003] The use of such a narrow frequency rage for speech transmissionsreduces naturalness and intelligibility of the speech when presented atthe receiving end. Therefore, wideband speech was introduced, whichprovides a better speech quality to the user of the receiving terminal.Wideband speech codecs (compressor/decompressor) were standardized e.g.in ITU-T G. 722, which specifications extend the bandwidth to up to 8kHz with a sampling frequency of 16 kHz. Current wideband speechtransmissions, however, requires bit-transparent end-to-end connections,e.g. by ISDN (Integrated Services Digital Network). Only tandem-freeoperation (TFO) or transcoder-free operation (TrFO) connections betweentwo wideband terminals allow to fully utilize the wideband terminalcapabilities. In addition, it requires special terminals equipped atboth transmission ends with the same wideband codecs. These restrictionshave limited to date the utilization of wideband speech.

[0004] In the future, the importance of wideband speech will increase,as the forthcoming adaptive multirate wideband (AMR-WB) speech codec,standardized in various 3GPP specifications, will be taken into use forthe 2G (second generation) and 3G (third generation) networks. But alsoAMR-WB will require bit-transparent tandem free operation and AMR-WBcapable terminals.

[0005] To date, the majority of terminals moreover still uses narrowbandspeech transmissions, and each connection between a wideband terminal onthe one hand and a narrowband terminal on the other hand is narrowband.In order to establish e.g. a call between an AMR-WB capable and aconventional narrowband (NB) terminal, like a PSTN (Public SwitchedTelephone Network) or a PLMN (Public Land Mobile Network) terminal,either the coding method needs to be negotiated in a way that the AMR-WBterminal shall use a narrow band codec, or AMR-WB speech frames need tobe transcoded into narrowband speech and vice versa in the network. Inboth cases the user of a receiving AMR-WB terminal will experiencenarrowband speech. Thus there will be an annoying quality differencebetween AMR-WB to AMR-WB and narrowband to AMR-WB calls. This furtherreduces the benefits gained with wideband terminals, until suchterminals become widely available.

[0006] The same problems are encountered also with narrowband servicesaccessed by a user of a wideband terminal, e.g. announcements, voicemail systems, interactive voice interfaces and narrowband audiostreaming applications. In case speech-based network services are to beprovided for both, wideband and narrowband terminals, the storagecapacity required for storing speech samples for both terminal types ismoreover tripled compared to the conventional narrowband case.

[0007] Another problem with the transmission of wideband audio signalsresults from the fact that the extended audio bandwidth used by thewideband terminals requires more transmission capacity. Morespecifically, the transmission capacity requirements are doubled forequal speech coding schemes. In addition, the adoption of widebandspeech transmission in wireless communications network is difficult dueto the lack of established wideband codecs for telecommunicationnetworks.

SUMMARY OF THE INVENTION

[0008] It is an object of the invention to improve the interoperabilitybetween units capable of handling wideband audio signals and units ornetwork components capable of handling narrowband audio signals.

[0009] It is moreover an object of the invention to achieve a betteraudio quality when narrowband audio signals are transmitted to areceiving unit capable of handling wideband audio signals.

[0010] On the one hand, a method for transcoding an audio signal in acommunications system is proposed, for which method the audio signal issupposed to be transmitted to a receiving unit via a communicationsnetwork. The proposed method comprises as first step receiving an audiosignal in a network element of the communications network. In a secondstep of the method, it is determined in the network element whether atranscoding of the received audio signal is required. The decision isbased on the kind of the received signal and on the capabilities of thereceiving unit and/or the capabilities of an interconnect networkinterconnecting the network element with the receiving unit. Then, areceived narrowband audio signal is converted into a wideband audiosignal in the network element, in case the received audio signal is anarrowband audio signal and in case it was determined that anarrowband-to-wideband transcoding of the received signal is required.Finally, the generated wideband audio signal is forwarded to thereceiving unit.

[0011] On the other hand, a transcoder for a network element of acommunications network is proposed which comprises means for convertinga received narrowband audio signal into a wideband audio signal. Whethera transcoding is actually performed depends on an indication from withinsaid network element that a narrowband-to-wideband transcoding of areceived signal is required. The indication might even be generatedwithin the transcoder itself.

[0012] Moreover, a network element for a communications network isproposed, which comprises in addition to the proposed transcoderprocessing means for determining whether a transcoding of a receivedaudio signal is required based on the kind of the received audio signaland on the capabilities of the receiving terminal and/or thecapabilities of an interconnect network interconnecting the networkelement with a receiving unit. Further, the network element comprisesmeans for forwarding audio signals to a receiving unit. Equally proposedis a wireless communications network with such a network element.

[0013] Finally, a communications system is proposed which comprises acommunications network with the proposed network element, and inaddition at least one unit capable of handling narrowband audio signalsand at least one further unit capable of handling wideband audiosignals. The two units can be interconnect via said communicationsnetwork. The device capable of transmitting narrowband audio signals canbe in particular either a server presenting services to a receivingterminal or another terminal, e.g. a mobile terminal. An alternativelyproposed communications network comprises at least two units capable ofhandling wideband audio signals, which can be interconnected via awireless communications network comprising the proposed network element.

[0014] The invention proceeds from the idea that a transcoding of anarrowband audio signal into a wideband audio signal can be implementedadvantageously in a network element of a communications system. Byintegrating all the load caused by a transcoding and also the decisionwhether a transcoding is needed in a network element of a communicationssystem, the interoperability of units capable of handling wideband audiosignals and units or network components capable of handling narrowbandaudio signals can be improved.

[0015] It is an advantage of the invention that an extra signaling forthe transcoding during a call setup or forwarding can be avoided.Terminals and other units can moreover be more simple as they do notneed to know and transcode many different codecs. Thus, any terminal orother unit can be employed in the communication according to theinvention without requiring extra functionalities. Further, terminalsusually also have only a restricted capacity available, and it is easierto provide the processing capacity needed in the network.

[0016] Preferred embodiments of the invention become apparent from thesubclaims.

[0017] Preferably, the transcoding comprises generating an at leastpartially artificial wideband audio signal based on the receivednarrowband audio signal. This way, the frequency range missing innarrowband audio signals can be supplemented artificially whenconverting a narrowband audio signal into a wideband audio signal. Thewideband audio signal provided to the receiving unit is thus at leastpartially artificial, but since it is proposed to be generated based onthe received narrowband signal, it can be close to the original audiosignal. Therefore, the invention allows to provide high quality audiosignals, in particular high quality speech, for a wideband terminaluser.

[0018] Since a received narrowband audio signal is usually transmittedin coded form, the coded signal is advantageously first decoded to alinear narrowband audio signal before it is converted. After conversionto a linear wideband audio signal, the signal can then be encoded againbefore it is forwarded to the receiving unit.

[0019] The generation of at least partially artificial wideband signalsout of received narrowband signal can be carried out in different ways.It can be based in particular on a statistical evaluation of thereceived narrowband signals, e.g. by using dedicated codebooks fornarrowband and wideband signals and by mapping narrowband codebookvalues to wideband codebook values for creating a spectrum shapingfilter. Alternatively, other statistical mapping methods can beemployed. The artificial wideband signal can also based on anup-sampling narrowband audio signals and a subsequent frequency shaping,or on spectral foldings of narrowband audio signals.

[0020] Preferably, the transcoder of the invention comprises in additionto the means for converting a received narrowband audio signal into awideband audio signal-means for converting a received wideband audiosignal into a narrowband audio signal. The latter means can then beemployed in case it was determined that a wideband-to-narrowbandtranscoding is necessary, whenever an audio signal is to be transmittedfrom a wideband unit to a narrowband unit. This ensures that thetranscoder can be employed bi-directionally, which further improves theinteroperability between different units. Accordingly, a negotiation ofa common narrowband codec in involved units during call setup or callforwarding is not needed. It also enables calls in cases in which acommon narrowband codec cannot be found. The method of the invention canbe extended accordingly to cover a transcoding in both directions.

[0021] The receiving unit employed according to the invention cantherefore be in particular a wideband terminal, a narrowband terminal ora speech-based network service equipment.

[0022] Advantageously, also a received wideband audio signal is firstdecoded to a linear wideband audio signal before it is converted to alinear narrowband audio signal. The linear narrowband audio signal isthen encoded before it is forwarded to the receiving narrowband unit.The conversion can comprise a lowpass filtering of the linear widebandaudio signal and a down-sampling of the lowpass filtered wideband audiosignal, in order to achieve an alias distortion free narrowband audiosignal.

[0023] Alternatively, the coded wideband speech could be converteddirectly to a coded narrowband audio signal in the speech parameterdomain, i.e. without decoding and encoding in the transcoder. However,this requires that the narrowband and the wideband codec are of the sametechnology family, e.g. an AMR-narrowband codec and an AMR-widebandcodec. By employing a parameter domain conversion, some of theparameters within the codec need to be converted, e.g. spectrum andexcitation parameters. Other parameters need no or only minoradjustments, e.g. pitch and gain parameters. This approach can be usedequally for narrowband to wideband conversions and for wideband tonarrowband conversions. A narrowband to wideband conversion in theparameter domain can but does not have to include an artificialbandwidth expansion.

[0024] The invention is particularly suited for four differentsituations.

[0025] In a first situation, a PSTN (public switched telephone network)narrowband terminal is connected via a communications network with awideband terminal. The wideband terminal can be in particular a mobilewideband terminal, in which case the communications network is formed byan interconnect network and in addition a wireless communicationsnetwork to which the wideband terminal is connected. If a narrowbandaudio signal addressed to the wideband terminal is transmitted by thePSTN terminal via the communications network, the narrowband audiosignal is converted to an at least partially artificial wideband audiosignal in a network element of the communications network. In case thewideband terminal is a mobile terminal, the network element ispreferably a network element of the wireless communications network towhich the wideband terminal is connected.

[0026] Also in the three other situations, the transcoding will becarried out advantageously in a network element of a wirelesscommunications network, e.g. a GSM (Global System for MobileCommunications) or a UMTS (Universal Mobile Telecommunications System)network.

[0027] In the second situation, audio signals are to be transmitted froma narrowband terminal to a wideband terminal. By providing an artificialbandwidth expansion in a network element of the communications networkvia which signals are transmitted from the narrowband terminal to thewideband terminal, the user of the wideband terminal can immediatelyutilize the wideband capabilities of the terminal. Thus, theinter-operability between wideband and narrowband terminals is improved.For the case that the narrowband terminal is to be employed as receivingunit, the network element should further include means for convertingwideband audio signals into narrowband audio signals. The transcoding ineither direction is preferably carried out close to the widebandterminal in order to avoid the necessity of transmitting wideband signalon the entire transmission path.

[0028] In the third situation, audio signals are to be transmittedbetween a wideband terminal as receiving unit and a speech-based networkservice equipment. If an artificial bandwidth expansion is provided in anetwork element of the communications network employed for transmittingthe audio signals to the wideband terminal as receiving unit, onlynarrowband speech samples need to be stored in the network serviceequipment. Also existing narrowband speech-based network serviceequipment can thereby be accessed by wideband terminals without asignificant reduction of subjective speech quality. Corresponding to thesecond situation, for the case that the service equipment is employedduring a connection exclusively or in addition as receiving unit, thenetwork element should further include means for converting widebandaudio signals into narrowband audio signals. The transcoding in eitherdirection is again preferably carried out close to the wideband terminalin order to avoid the necessity of transmitting wideband signal on theentire transmission path.

[0029] In the fourth situation audio signals are to be transmittedbetween two wideband terminals, where it is preferred to transmit theaudio signals at least in a part of the interconnecting network ornetworks as narrowband signal. By combining bandwidth reduction, e.g.low-pass filtering, and artificial bandwidth expansion in a networkelement of each of the wireless communications networks to which therespective wideband terminal is connected, a wideband audio signal canbe converted into a narrowband audio signal at the beginning of thetransmission path and converted back into a wideband audio signal at theend of the transmission path. Thus, the operator is able to transmitwideband speech with little transmission capacity, in particular alsousing existing trunking networks, without a significant reduction of thespeech quality perceived by the users of the wideband terminals.

[0030] The network element of the invention can be any network elementwhich has access to traffic channels of a circuit switched network orwhich has access to the user plane of a packet network. If it is anetwork element of a wireless communications network, it can be forinstance a network element of a GSM BSS (Base Station Subsystem), of aRAN (Radio Access Network), or of a core network. The network elementshould moreover have enough signal processing capacity to carry out thetranscoding according to the invention. Therefore, the network elementaccording to the invention can be in particular, though not exclusively,a transcoder unit of 2G networks, a transcoder unit of 3G networks, amedia gateway enabling the inter-working of user data between packet andcircuit switched networks, a multi resource function in all-IP (InternetProtocol) networks, an announcement device in any network, aninteractive voice interface device, or a streaming server in packetnetworks.

BRIEF DESCRIPTION OF THE FIGURES

[0031] In the following, the invention is explained in more detail withreference to drawings, of which

[0032]FIG. 1 is a high-level block diagram of an embodiment of thecommunications system of the invention;

[0033]FIG. 2 is a block diagram illustrating a first embodiment of anarrowband-to-wideband conversion according to the invention; and

[0034]FIG. 3 is a block diagram illustrating a second embodiment of anarrowband-to-wideband conversion according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0035]FIG. 1 schematically shows selected elements of an embodiment ofthe communications system according to the invention.

[0036] In the system, a communications network comprises in one of itsnetwork elements a transcoder 1. Of the network, which can either be acircuit switched or a packet switched network, only the transcoder 1 isdepicted. The system further comprises a wideband terminal 2 and anarrowband terminal 3. The network element with the transcoder 1 hasaccess to traffic channels 11, 12, 21, 22 established respectivelybetween the terminals 2, 3 and the network for uplink and downlinktransmissions.

[0037] The wideband terminal 2 includes a wideband encoder 13 and awideband decoder 24. The narrowband terminal 3 includes correspondinglya narrowband encoder 23 and a narrowband decoder 14. The transcoder 1includes on the one hand a wideband decoder 15 connected via awideband-to-narrowband converter 16 to a narrowband encoder 17. On theother hand, the transcoder 1 includes a narrowband decoder 25 connectedvia a narrowband-to-wideband converter 26 to a wideband encoder 27.

[0038] The depicted part of the communications system functions asfollows:

[0039] In a first situation, speech is to be transmitted from thewideband terminal 2 to the narrowband terminal 3. The wideband terminal2 encodes the speech in the integrated wideband encoder 13 in order toobtain an encoded wideband signal. The encoded signal is thentransmitted to the transcoder 1 via the physical channel 11 establishedfor uplink transmissions between the wideband terminal 2 and thenetwork.

[0040] In the transcoder 1, the received wideband signal is firstdecoded by the wideband decoder 15 in order to obtain a linear widebandsignal. The linear wideband signal is subsequently converted by thewideband-to-narrowband converter 16 to a linear narrowband signal. As alast step performed in the transcoder 1, the narrowband encoder 17encodes the obtained linear narrowband signal.

[0041] The encoded narrowband signal is transmitted by the network tothe narrowband terminal 3 via a downlink channel 12 established betweenthe network and the narrowband terminal 3. The narrowband terminal 3 nowdecodes the received narrowband signal with its narrowband decoder 14for presentation to a user.

[0042] In a second situation, speech is to be transmitted in theopposite direction, i.e. from the narrowband terminal 3 to the widebandterminal 2. In this case, the narrowband terminal 3 encodes the speechthat is to be transmitted with the integrated narrowband encoder 23. Theresulting signal is transmitted to the network element with thetranscoder 1 via the uplink channel 21 established between thenarrowband encoder 23 and the network.

[0043] In the network element, the narrowband decoder 25 of thetranscoder 1 decodes the received signal to a linear narrowband signal.Further, the narrowband-to-wideband converter 26 of the transcoder 1converts the linear narrowband signal to a linear wideband signal. Theconversion includes a generation of an artificial linear wideband signalout of the linear narrowband signal. The linear wideband signal isencoded again by the wideband encoder 27 of the transcoder 1 andforwarded to the wideband terminal 2 via downlink channel 22 establishedbetween the network and the wideband terminal 2.

[0044] In the wideband terminal 2, the wideband decoder 24 decodes thereceived signals to linear wideband signals for presenting them to auser.

[0045] Thus, the depicted system enables bi-directional transmissions ofspeech signals between the wideband terminal 2 and the narrowbandterminal 3.

[0046] Selected possibilities of generating artificial wideband signalsduring a narrowband-to-linear conversion will now be described withreference to FIGS. 2 and 3.

[0047]FIG. 2 is a schematic block diagram of a first embodiment of thenarrowband-to-wideband converter 26 of FIG. 1. The converter 26 of thisembodiment comprises means for up-sampling 31 and means for frequencyshaping 32.

[0048] In the first embodiment, the linear narrowband signal isup-sampled without low-pass filtering by the means for up-sampling 31.This generates alias frequency components of the narrowband signal ontothe upper band of the wideband signal, i.e. a mirror image of thenarrowband signal in the frequency domain. This aliased wideband signal,however, contains excessive distortion which would be subjectivelyannoying for the user of the receiving wideband terminal 2. Thereforethe distortions are smoothed in the means for frequency shaping 32 byattenuating dynamically aliased components based on the narrowbandsignals. It is to be noted that in particular more attenuation is neededfor aliased components with voiced phonemes than for those with unvoicedphonemes.

[0049] Another possibility of converting linear narrowband signals tolinear wideband signals is presented in FIG. 3, which illustrates, inform of a schematic block diagram, a second embodiment of thenarrowband-to-wideband converter 26 of FIG. 1.

[0050] The second embodiment of the narrowband-to-wideband converter 26comprises a first processing branch with means 33, 34 for up-samplingand lowpass filtering received signals. A second processing branchincludes means for a narrowband analysis 35 and means for an upper bandsignal generation 36. The output of both processing branches isconnected to summing means 37, which form the output of thenarrowband-to-wideband converter 26 of FIG. 1.

[0051] In the first processing branch of the converter 26, the linearnarrowband signal is first up-sampled and then low-pass filtered by thecorresponding means 33, 34 in order to obtain a distortion free linearwideband signal of a lower frequency band.

[0052] In the second processing branch of the converter 26, the upperfrequency band of the wideband signal is statistically recovered byusing the spectral characteristics of the frequency components of thereceived narrowband signal.

[0053] The means for a narrowband analysis 35 in the second processingbranch first perform a spectrum analysis of the received narrowbandsignal. The means for upper band signal generation 36 have access to astored codebook of narrowband speech spectral parameters and to acorresponding stored codebook of upper band wideband speech spectralparameters. The means for upper band signal generation 36 are thereforeable to perform a mapping between narrowband and wideband codebookvalues, wherein the required narrowband codebook values are calculatedfrom the spectrum analysis of narrowband signal. The mapping is thussuited for predicting the upper band spectrum of wideband speech basedon the received narrowband signal. The upper band signal is generatedmore specifically by shaping upper band excitation signal with aspectrum-shaping filter which is defined by the determined widebandcodebook values. The upper band excitation signal can be a locallygenerated noise or pulse excitation, like in a linear prediction coding(LPC) based speech codec. Alternatively, the upper band excitationsignal could be a mirror image of the narrow band signal, like in thefirst embodiment, or a frequency shaped mirror image.

[0054] In order to obtain finally the complete wideband signal, theartificially generated upper band signal output by the second processingbranch is added by the means for summing 37 to the lower band signaloutput by the first processing branch.

[0055] The wideband-to-narrowband conversion in thewideband-to-narrowband converter 16 of FIG. 1 can be realized forexample by lowpass filtering the linear wideband signal and by thendown-sampling the low-pass filtered wideband signal. The result is analias distortion free narrowband signal.

[0056] In both directions, the transcoding can equally be achieved withother suitable methods, as long as the transcoding of a narrowbandsignal to a wideband signal results in an at least partially artificialwideband signal of a broader frequency range than the originalnarrowband signal.

[0057] With reference to FIGS. 4, 5 and 6, three different situationswill now be presented, in which the invention can be employedadvantageously. Corresponding elements are referred to in these figuresby the same reference signs.

[0058]FIG. 4 is a schematic block diagram of a communications system andillustrates a first situation in which audio signals are to betransmitted between a wideband terminal and a narrowband terminal. Thesystem basically corresponds to the system of FIG. 1, only the networkpart being depicted in more detail. In FIG. 4, a wideband terminal 0.40has access to a first UTRAN-RAN (radio access network) or a GSM-BSS(base station system) 41. The first RAN or BSS 41 is connected via afirst core network with a first network element 42, via an interconnectnetwork 43 and via a second core network with a second network element44 to a second RAN or BSS 45. A narrowband terminal 46 has access to thesecond RAN or BSS 45. The depicted network elements 42, 44 are botheither a 3G media gateway MGW or a 2G transcoder TC, which are employedin core networks for performing the transcoding between different speechcoding schemes. The first network element 42 comprises means 47 forartificial bandwidth expansion of received narrowband audio signals, andmeans 48 for bandwidth reduction of received wideband audio signals.Transmissions between the wideband terminal 40 and the narrowbandterminal 46 are indicated in the figure by arrows.

[0059] A wideband audio signal transmitted by the wideband terminal 40and addressed to the narrowband terminal 46 of FIG. 4 is received by thefirst RAN or BSS 41 and forwarded to the depicted network element 42 ofthe connected core network. In the network element 42, the widebandaudio signal is subject to a bandwidth reduction in order to obtain anarrowband audio signal. The bandwidth reduction is achieved by themeans 48 for bandwidth reduction, for example as mentioned above byemploying a lowpass filtering. The narrowband audio signal is thentransmitted via the interconnect network 43, the second network element44 of the second core network and the second RAN or BSS 45 to thenarrowband terminal 46. The narrowband terminal 46 is able to presentthe received narrowband audio signal to a user.

[0060] In the opposite direction, a narrowband audio signal transmittedby the narrowband terminal 46 and addressed to the wideband terminal 40of FIG. 4 is received by the second RAN or BSS 45 and forwarded to thedepicted network element 44 of the connected core network. Thenarrowband audio signal is then further transmitted via the interconnectnetwork 43, to the network element 42 of the first core network. In thisnetwork element 42, an artificial wideband audio signal is generated bythe means for bandwidth extension 47 out of the received narrowbandaudio signal, e.g. according to one of the methods described withreference to FIGS. 1 to 3. The generated wideband audio signal is thenforwarded via the first RAN or BSS 41 to the wideband terminal 40. Thewideband terminal 40 is able to present the received audio signal to auser without subjective reduction of speech quality compared to receivedoriginal wideband speech.

[0061]FIG. 5 illustrates a second situation in which audio signals areto be transmitted between terminals and a speech-based network serviceequipment. The figure shows a communications system which corresponds tothe system of FIG. 4, except that both terminals 40, 46 have in additionaccess to a speech-based network service equipment 50 via the respectiveRAN or BSS 41, 45, the respective core network with network element 42or 44 and the interconnect network 43. The speech-based network serviceequipment 50 only stores narrowband speech samples and is only designedfor handling narrowband audio signals.

[0062] Transmissions between the speech-based network service equipment50 and the narrowband terminal 46 are carried out in either directionvia the interconnect network 43, the second network element 44 of thesecond core network and the second RAN or BSS 45 without a transcodingaccording to the invention.

[0063] Transmissions between the speech-based network service equipment50 and the wideband terminal 40 are indicated in the figure by arrows.They are carried out via the interconnect network 43, the first networkelement 42 of the first core network and the first RAN or BSS 41, or inreversed order respectively. In this case, however, wideband audiosignals originating from the wideband terminal 40 are reduced inbandwidth by the corresponding means 48 of the first network element 42to form a narrowband audio signal, and narrowband audio signalsoriginating from the speech-based network service equipment 50 areexpanded to artificial wideband audio signals by the corresponding means47 of the first network element. The processing is thus analogous to theprocessing in the situation of FIG. 4.

[0064] It depends on the respective application whether a bandwidthreduction, an artificial bandwidth expansion or both are required in thenetwork element 42 of the first core network.

[0065] In the situation of FIG. 5, instead of a speech-based networkservice equipment 50, also a PSTN narrowband terminal could be connectedto the interconnect network 43. In order to enable a communicationaccording to the invention between such a PSTN narrowband terminal andthe depicted wideband terminal 40, a processing corresponding to theprocessing described with reference to FIG. 5 for the communicationinvolving a speech-based network service equipment 50 can be employed.

[0066] In a last presented situation, signals are to be transmittedbetween two wideband terminals. FIG. 6 therefore shows a communicationssystem which corresponds again largely to the system of FIG. 4, exceptthat in this communications system, both terminals 40, 60 are widebandterminals. The first wideband terminal 40 is connected to the first RANor BSS 41 as in FIG. 4, and the second wideband terminal 60 is connectedto the second RAN or BSS 45 as the narrowband terminal in FIG. 4. Theinterconnect network 43 of the system of FIG. 6 is moreover supposed tobe a trunking network which was exclusively designed for transmittingnarrowband signals. In the system of FIG. 6, also the second networkelement 44 comprises means 61 for artificial bandwidth expansion ofreceived narrowband audio signals, and means 62 for bandwidth reductionof received wideband audio signals.

[0067] In the system of FIG. 6, it is not different kinds of unitsemployed for transmitting and receiving audio signals which make atranscoding necessary, since both involved units 40, 60 are widebandterminals. Rather, a transcoding is employed for enabling a low capacitytransmission via the trunking network 43.

[0068] Thus, whenever the first wideband terminal 40 transmits awideband audio signal addressed to the second wideband terminal 60, theaudio signal is forwarded via the first RAN or BSS 41 to the firstnetwork element 42, where it is processed a first time. Morespecifically, the means 48 for bandwidth reduction of the first networkelement 42 are employed for generating based on the received widebandaudio signal a narrowband audio signal, which can be transmitted by theemployed interconnect network 43. The interconnect network 43 forwardsthe narrowband audio signal to the second network element 44 of thesecond core network. The means 61 for artificial bandwidth expansion ofthe second network element 44 convert the received narrowband audiosignal artificially into a wideband audio signal again. The widebandaudio signal is forwarded via the second RAN or BSS 45 to the secondwideband terminal 60. For bandwidth reduction and expansion, for examplethe methods described with reference to FIGS. 1 to 3 can be employed,just as for the situations illustrated in FIGS. 4 and 5. By thisproceeding, the second wideband terminal 60 can be supplied withwideband speech via the trunking network 43 without a significantreduction of subjective speech quality.

[0069] In the opposite direction, the processing is exactly the same, abandwidth reduction of a transmitted wideband audio signal being carriedout by the corresponding means 62 of the second network element 44, anda generation of an artificial wideband audio signal by the correspondingmeans 47 of the first network element 42.

[0070] The methods for artificial bandwidth generation employed in theabove described embodiments of the invention are to be understood asexemplary methods. Any other suited method can be utilized instead.

1-34. (Cancelled).
 35. Method for transcoding an audio signal in acommunications system, which audio signal is to be transmitted to areceiving unit via a communications network, said method comprising:receiving an audio signal in a network element of said communicationsnetwork; determining in said network element based at least on the kindof the received signal and on the capabilities of said receiving unitwhether a transcoding of the received audio signal is required; in casesaid received audio signal is a narrowband audio signal and in case itwas determined that a narrowband-to-wideband transcoding of the receivedsignal is required, converting said received narrowband audio signalinto a wideband audio signal in said network element, and forwarding thegenerated wideband audio signal to the receiving unit.
 36. Methodaccording to claim 35, wherein said network determines whether atranscoding of the received audio signal is required in addition basedon the capabilities of an interconnect network interconnecting saidnetwork element with said receiving unit.
 37. Method according to claim35, wherein said receiving unit is a wideband terminal, a narrowbandterminal or a speech-based network service equipment.
 38. Methodaccording to claim 35, wherein a received narrowband audio signal isconverted into a wideband audio signal in said network element bygenerating an at least partially artificial wideband audio signal basedon the received narrowband audio signal.
 39. Method according to claim35, wherein said received audio signal is an encoded audio signal,wherein a received narrowband audio signal is decoded before beingconverted to a wideband audio signal, and wherein a generated widebandaudio signal is encoded before being forwarded to the receiving unit.40. Method according to claim 35, wherein converting a receivednarrowband signal comprises up-sampling the received narrowband audiosignal and frequency shaping the up-sampled signal in a way suited tosmooth distortions resulting in the up-sampling.
 41. Method according toclaim 35, wherein converting a received narrowband audio signalcomprises up-sampling the received narrowband audio signal and lowpassfiltering the up-sampled signal in order to obtain a lower band signal;generating an artificial upper band signal based on a statisticalevaluation of the received narrowband audio signal; and combining theobtained lower band signal with the generated upper band signal to awideband audio signal.
 42. Method according to claim 41, wherein theartificial upper band signal is generated by performing a spectralanalysis of a received narrowband audio signal and by mapping resultingnarrowband codebook values to wideband codebook values, the widebandcodebook values forming a spectrum-shaping filter used for shaping upperband excitation signal.
 43. Method according to claim 35, wherein saidreceived audio signal is an encoded audio signal, and wherein a receivednarrowband audio signal is converted without decoding to a codedwideband audio signal in the speech parameter domain.
 44. Methodaccording to claim 35, further comprising in case said received audiosignal is a wideband audio signal and in case it was determined that awideband-to-narrowband transcoding of the received signal is required,converting said received wideband audio signal into a narrowband audiosignal, and transmitting the generated narrowband audio signal to thereceiving unit.
 45. Method according to claim 44, wherein said receivedaudio signal is an encoded audio signal, wherein a received widebandaudio signal is decoded before being converted to a narrowband audiosignal, and wherein a generated narrowband audio signal is encodedbefore being forwarded to the receiving unit.
 46. Method according toclaim 44, wherein said received audio signal is an encoded audio signal,and wherein a received wideband audio signal is converted withoutdecoding to a coded narrowband audio signal in the speech parameterdomain.
 47. Method according to claim 35, wherein said network elementis a network element of a wireless communications network.
 48. Methodaccording to claim 35, wherein a receiving unit is capable of handlingwideband audio signals, wherein a narrowband audio signal is transmittedby a public switched telephone network terminal capable of handlingnarrowband audio signals and addressed to said receiving unit, whereinsaid narrowband audio signal is transmitted via said communicationsnetwork to said receiving unit, and wherein said narrowband audio signalis converted in a network element of said communications network to anat least partially artificial wideband audio signal before transmissionto said receiving unit.
 49. Method according to claim 35, wherein areceiving unit is capable of handling wideband audio signals, whereinsaid communications network comprises a wireless communications networkto which said receiving unit is connected, wherein a narrowband audiosignal is transmitted by a unit capable of handling narrowband audiosignals and addressed to said receiving unit, wherein said narrowbandaudio signal is transmitted via said wireless communications network tosaid receiving unit, and wherein said narrowband audio signal isconverted in a network element of said wireless communications networkto an at least partially artificial wideband audio signal fortransmission to said receiving unit.
 50. Method according to claim 35,wherein a receiving unit is capable of handling narrowband audiosignals, wherein a wideband audio signal is transmitted by atransmitting unit capable of handling wideband audio signals andaddressed to said receiving unit, wherein said communications networkcomprises a wireless communications network to which said transmittingunit is connected, wherein said wideband audio signal is to betransmitted via said wireless communications network to said receivingunit, and wherein said wideband audio signal is converted in a networkelement of said wireless communications network to a narrowband audiosignal for transmission to said receiving unit.
 51. Method according toclaim 35, wherein a receiving unit is capable of handling wideband audiosignals, wherein said communications network comprises a first wirelesscommunications network to which said receiving unit is connected,wherein a wideband audio signal is transmitted by a transmitting unitcapable of handling wideband audio signals and addressed to saidreceiving unit, wherein said communications network comprises a furtherwireless communications network to which said transmitting unit isconnected, wherein said first and said further wireless communicationsnetwork are interconnected by an interconnect network capable oftransmitting narrowband audio signals, wherein said wideband audiosignal transmitted by said transmitting unit is converted in a networkelement of said further wireless communications network into anarrowband audio signal for transmission to said first wirelesscommunications network via said interconnect network, and wherein saidnarrowband signal is converted in a network element of said firstwireless communications network to an at least partially artificialwideband audio signal for transmission to said receiving unit. 52.Network element for a communications network comprising: means forreceiving audio signals addressed at a receiving unit; processing meansfor determining whether a transcoding of the received audio signal isrequired based at least on the kind of the received audio signal and onthe capabilities of the receiving unit; transcoder for transcoding areceived audio signal, said transcoder comprising means for converting areceived narrowband audio signal into a wideband audio signal, in casesaid transcoder receives an indication from within said network elementthat a narrowband-to-wideband transcoding of a received signal isrequired; and means for forwarding audio signals to a receiving unit.53. Network element according to claim 52, wherein said processing meansdetermine whether a transcoding of the received audio signal is requiredbased in addition on the capabilities of an interconnect networkinterconnecting said network element and said receiving unit. 54.Network element according to claim 52, wherein said means of saidtranscoder for converting a received narrowband audio signal into awideband audio signal are means for converting said received narrowbandaudio signal into a wideband audio signal by generating an at leastpartially artificial wideband audio signal based on the receivednarrowband audio signal.
 55. Network element according to claim 52,wherein said transcoder further comprises decoding means for decoding areceived narrowband audio signal before it is converted by the means forconverting, and encoding means for encoding a generated wideband audiosignal to an encoded wideband audio signal.
 56. Network elementaccording to claim 52, wherein said means for converting of saidtranscoder comprise means for up-sampling a received narrowband audiosignal and means for frequency shaping said up-sampled signal in a waysuited to smooth distortions resulting in the up-sampling.
 57. Networkelement according to claim 52, wherein said means of said transcoder forconverting comprise means for up-sampling a received narrowband audiosignal and for lowpass filtering the up-sampled signal in order toobtain a lower band signal; means for generating an artificial upperband signal based on a statistical evaluation of the received narrowbandaudio signal; and means for combining the obtained lower band signalwith the generated upper band signal to a wideband audio signal. 58.Network element according to claim 57, wherein said means of saidtranscoder for generating an artificial upper band signal comprise aspectral analyzer for analyzing a received narrowband signal, and meansfor spectrum-shaping the analyzed signals with a filter for shapingupper band excitation, wherein said filter is created by mappingnarrowband codebook values obtained based on the spectral analysis towideband codebook values.
 59. Network element according to claim 52,wherein said means of said transcoder for converting a receivednarrowband audio signal into a wideband audio signal are means forconverting a received encoded narrowband signal into an encoded widebandsignal in the parameter domain.
 60. Network element according to claim52, wherein said transcoder further comprises means for converting areceived wideband audio signal into a narrowband audio signal in casesaid transcoder receives information from within said network elementthat a wideband-to-narrowband transcoding of a received signal isrequired.
 61. Network element according to claim 60, wherein saidtranscoder further comprises decoding means for decoding a receivedwideband audio signal before it is converted by the means forconverting, and encoding means for encoding a generated narrowband audiosignal to an encoded narrowband audio signal.
 62. Network elementaccording to claim 60, wherein said means of said transcoder forconverting a received wideband audio signal into a narrowband audiosignal are designed for converting a received encoded wideband signalinto an encoded narrowband signal in the parameter domain.
 63. Wirelesscommunications network comprising a network element according to claim52.
 64. Communications system comprising a first unit capable ofhandling narrowband audio signals, a second unit capable of handlingwideband audio signals, and a communications network with a networkelement according to claim 52, said first unit being interconnectablewith said second unit via said communications network. 65.Communications system according to claim 64, wherein said first unitcapable of handling narrowband audio signals is a public switchedtelephone network terminal capable of handling narrowband audio signals.66. Communications system according to claim 64, wherein said first unitcapable of handling narrowband audio signals is a narrowband terminalaccessing a first wireless communications network, wherein said secondunit capable of handling wideband audio signals is a wideband terminalaccessing a second wireless communications network, wherein said firstunit is interconnected with said second unit via said first wirelesscommunications network, an interconnect network and said second wirelesscommunications network, and wherein said network element is part of saidsecond wireless communications network.
 67. Communications systemaccording to claim 64, wherein said first unit capable of handlingnarrowband audio signals is a narrowband speech-based network serviceequipment connected to an interconnect network, wherein said second unitcapable of handling wideband audio signals is a wideband terminalaccessing a wireless communications network, wherein said first unit isinterconnected with said second unit via said interconnect network andsaid wireless communications network, and wherein said network elementis part of said wireless communications network.
 68. Communicationssystem comprising a first unit capable of transmitting wideband audiosignals, a second unit capable of receiving and handling wideband audiosignals, and a communications network comprising at least a firstwireless communications network, an interconnect network capable ofhandling narrowband audio signals, and a second wireless communicationsnetwork, wherein said first unit is interconnectable with said secondunit via said first wireless communications network, said interconnectnetwork, and said second wireless communications network, each wirelesscommunications network comprising a network element according to claim52.